There are several methods of collection and analysis of spores. In one method, the bare sides of a glass optical fiber are treated with a substance that adsorbs the target substance, causing a change in refractive index of the surface of the optical fiber. The change in refractive index changes how much light leaks out of the curved, treated segment, causing a change in signal received by the light receptor. However, any phosphorescent or fluorescent materials in contact with the sensor could distort readings by introducing a competing light source.
Another method uses fluorescence only to detect and identify a wide range of biological substances, and many biological substances other than spores fluoresce, potentially masking the presence of spores. The fluorescence is detectable only while the exciting light is on, and does not continue after the light is turned off.
One device for spore detection impacts the spores onto a reactive substrate on a filter wheel, and the substrate combines with certain portions of the spore to make phosphorescent products. The phosphorescent products allow the system to be very sensitive, detecting as few as 1000 spores in one spot. However, the device does not make use of the native phosphorescence of the spores.
Another device utilizes a Mie (Rayleigh) scattering and fluorescence of a continuous laser beam to identify each particle. Phosphorescence of the biological particle is not possible since the device does not view the particle after it leaves the point at which it is illuminated by the laser.
Another device measures multiple optical properties, including the refractive index and the size and fluorescence of each individual particle as it passes through the target zone. Each particle is identified from these properties. However, it does not use phosphorescence as a measurable characteristic.
Another method of spore detection concentrates spore particulates onto a spot prior to analysis. This is not a real-time method since the particulates need to be collected for a period of time, and the spot of particulates is rotated to the measurement device for a reading. Biological, chemical, and radiological properties of the particulates are identified.
Another method utilizes ultrafine fluorescent particles that are attached to target particles in the air stream. The attachment of the ultrafine particles to the target particles produces a change in the optical properties of the ultrafine fluorescent particles or the target particles, or both. The ultrafine particles are selected to be specific to a class of target particulates, such as biological particulates, or the ultrafine particles can be specific to a particular target particulate in cases of monitoring for the presence or absence of a single contaminant.
Another method utilizes a high intensity near-field light to form an optical trap to hold particles in place for a variety of optical and physical measurements. An interrogating light can be applied from an external light source to a trapped substance, in which small particles suspended in fluids move around randomly due to Brownian motion. However, a substance is subjected to a near-field optical trap for an extended period of time, and this method does not allow for measurement techniques in a dynamic system.